In recent years, products that combine the GIS (Geographical Information System) and the GPS (Global Positioning System), as represented by the car navigation system, have become significantly widespread. At the same time, application of location information by the GIS and the GPS to safe driving by the ITS (Intelligent Transport Systems) is expected, and location information of planimetric features on and the sides of roads is assumed to be efficient information.    Meanwhile, greater precision and sophistication of a road inventory that records information of planimetric features around roads is desired. However, since it is necessary to make a high-precision survey to draft the road inventory that records locations of the planimetric features on or the sides of roads, such as distance marks, traffic signs, guardrails, white lines, etc. on a one five-hundredth scale, static measurement using the GPS and a total station to measure distances and angles is performed. Additionally, there may exist about two thousand features as measurement subjects in intervals of 30 km in round trip in national roads. As a result, enormous cost and time is required for greater precision and sophistication of the road inventory in all parts of countries.    Therefore, in the aim of reducing time and cost to collect information, attention is focused on a MMS (Mobile Mapping System), and research and development is performed on the MMS.
The MMS is a system wherein a measurement vehicle (called vehicle below) equipped with devices such as an odometry device, a gyroscope, a GPS antenna connected to a GPS receiver, a laser radar, and a camera, etc. runs roads to obtain locations of planimetric features, etc. around the roads and map information from the running vehicle. The odometry device calculates distance data indicating a travel distance of the vehicle by carrying out the odometry method.    As to the gyroscope, angular velocity data indicating the inclination of the vehicle in three-axial directions (pitch, roll, yaw angles) is calculated by mounting three gyroscopes, for example.    The GPS calculates positioning data indicating a running position (coordinate) of the vehicle.    The camera takes pictures or videos and outputs time-series image data.    The laser radar calculates direction and distance data indicating distances to a road surface in each direction.    The measuring unit of the MMS calculates a location of a feature designated by a user based on these distance data, angular velocity data, positioning data, image data, direction and distance data, etc.
The gyroscope, the GPS antenna, the laser radar, and the camera are all mounted on a top board of the vehicle and obtain various types of data. The top board is a frame made up of plural pillar-shaped members, and due to limited size of the top board of the vehicle, these devices are placed near to one another. However, when devices large in size like the camera and the laser radar are installed near the GPS antenna, the GPS antenna is placed behind these devices, so that the reception range is limited, which results in unstable reception of radio waves from a GPS satellite. For example, it may happen that by the vehicle turning an intersection, a radio wave which has been received to date is blocked by camera equipment and cannot be received.
As a countermeasure for this, it is considered a method to install the GPS antenna at higher position by using a supporting column, etc. so that a reception plane of the antenna is placed above the level of the other devices (see Patent literature 1, for example).
Patent literature 1: Japanese Unexamined Patent Publication No. 2007-218705